1. Field of the Invention
The present invention relates to a cleaning machine, in particular a dishwasher which has a cleaning chamber, in which cleaning machine the items to be cleaned are cleaned in line with a program sequence of pre-washing, cleaning and drying steps, in particular for commercial use.
2. Description of the Background Art
In dishwashers in which the washware is not transported during the cleaning process and in which the cleaning steps proceed in accordance with a predefined program, a distinction is drawn between two basic variants:
Firstly, dishwashers with a tank system in which a washing liquid is stored are known. The washware which is continuously introduced is cleaned with this washing liquid, without said washing liquid being discarded after a cleaning cycle. Following the cleaning process, fresh water which has been heated in a boiler or a flow heater is applied to the washware via an additional rinsing system. All or some of this introduced rinse water is used to regenerate the washing liquid. These machines with a two-circuit system are mainly used in commercial operations since very short cycle times, for example of less than 60 seconds up to a few minutes, can be achieved with said machines.
Secondly, dishwashers with water replacement systems are known. In machines which are operated in accordance with this principle, fresh water is used in each cleaning cycle for the method steps of cleaning and rinsing, or the wash water from the first cleaning cycle is used as cleaning liquid for the second cleaning cycle and is then discarded. These machines are mainly used in the domestic sector. The respective replacement of the washing liquid and/or rinsing solution and the associated heating of the liquids result—compared to dishwashers with a two-circuit system—in longer cycle times, for example of up to more than 2 hours.
Single-chamber systems of this type are often designed as “front loaders” and have a washing chamber with a front flap which is to be opened in order to load washware into and unload washware from the washing chamber. Dishwashers of this type can be designed for various purposes and may be used, for example, as free-standing appliances or else as under-counter appliances.
DE 299 23 594 U1 discloses, for example, a commercial dishwasher with a two-circuit system. This dishwasher comprises at least one washing chamber and in each case a wash water tank which is associated with each washing chamber. A heating device for the wash water in the wash water tank and a circulation pump for the wash water with a motor drive may be provided. Said circulation pump takes in heated wash water from the wash water tank via an intake line and supplies said wash water, via at least one pressure line, to spray nozzles of at least one spray device, in order to spray wash water onto the washware. Said washware is accommodated on a mount within the washing chamber. An air supply device which is integrated in the intake line of the circulation pump is provided. Also present is a control device which permits air to be supplied only during the starting phase of the washing process with hot water.
Peltier elements and their manner of operation are known. A document which was downloaded from the Internet site http://de.wikipedia.org/wiki/Peltier-Element on Feb. 13, 2008 describes the structure and manner of operation of a Peltier element. A Peltier element comprises two or more small cuboids in each case composed of p- and n-doped semiconductor material (bismuth telluride, Bi2Te3, silicon germanium) which are connected to one another alternately at the top and at the bottom by metal bridges. The metal bridges at the same time form the thermal contact areas and are insulated by an applied film or foil or a ceramic plate. Two different cuboids are always connected to one another such that they produce a series circuit. The supplied electric current flows through all the cuboids in succession. Depending on the current intensity and direction, the upper connection points cool down, whereas the lower connection points heat up. The current therefore pumps heat from one side to the other and creates a temperature difference between the plates.
The most common form of Peltier element comprises two usually square plates composed of Al2O3 ceramic (aluminum oxide) with an edge length of 20 mm to 90 mm and a gap of from 3 mm to 5 mm, between which plates the semiconductor cuboids are soldered in. To this end, the ceramic surfaces are provided on their mutually facing surfaces with metal faces which can be soldered.
If the warm side is cooled down, for example by means of a mounted heat sink with a fan, the cooling side becomes even colder. The temperature difference between the two sides can be, depending on the element and the current, up to approximately 69 Kelvin in the case of one-stage elements.
Applications of Peltier elements in conjunction with dishwashers are likewise known. DE 103 34 792 A1, for example, describes a domestic dishwasher of known design, that is to say with water replacement, which is additionally equipped with a device for drying the dishes which have been cleaned and rinsed. In this device, air is taken from the washing chamber, conducted past the cold side of a Peltier element, and thus dried. The dried air is again conducted into the washing chamber. The air in the interior of the washing chamber is heated using the waste heat from the Peltier element.
Further known applications of Peltier elements in conjunction with dishwashers always concern the dissipation of heat from the air of the interior and thus deliberate condensation of the contained moisture.
The conventional dishwashers, however, have the disadvantage that the thermal energy which is located in the waste water has not been used further by the dishwasher or its working processes.
In the case of water replacement machines, this would be, for example per washing cycle, the heat content of 2×10 l of water at a temperature of 50-60° C. In the case of dishwashers with a two-circuit system, it can be, for example per washing cycle, 2.5 l of water at a temperature of 60° C. This quantity likewise adds up to an appreciable volume, and thus to a considerable heat content, over the number of washing cycles per working day.
When batch dishwashers with waste water heat recovery have been disclosed to date, tube heat exchangers of conventional design were used in the process. In addition to a modest effect, these had the disadvantages of high susceptibility to soiling and a lack of controllability.